1. Technical Field
This invention relates to surgery, and more particularly to electrodes for surgical resectoscopes.
2. Background Information
A variety of resectoscopes have been developed and are known for purposes of tissue resection. Common applications are in cystoscopy and, more recently, in hysteroscopy. The use of resectoscopes in a variety of other applications is an evolving area.
A main component of a resectoscope is commonly referred to as "the working element". The working element comprises an electrode mounted into a reciprocating mechanism that can be moved forward and backward between retracted and extended positions. The electrode includes a distal tip and one or more conductors extending longitudinally back through the sheath. In the retracted position the electrode tip resides within an outer sleeve or tube which protects the tip from interaction with the patient's body and vice versa. In the extended position, the electrode tip extends forward of the end of the protective sleeve for engaging the patient's tissue. The mechanism may either be passive or spring loaded. In the latter case, a typical configuration involves the spring biasing the electrode into the retracted position.
For visualization of the interaction of the electrode with the patient's tissue, an optical element is typically inserted within the sheath. The optical element, often referred to as the "telescope" has a typical diameter of approximately 4 mm. Depending on the application and the preferences of the surgeon, the telescope may be provided with a variety of depths and angles of view. For prostate resection and other urologic applications, angles of up to 120.degree. are often preferred. In uterine applications, preferred angles of view may vary between 0.degree. and 30.degree.. A depth of field is typically infinite, with a focal length of approximately 2 cm. Such a focal length may cause size distortions but provides the skilled surgeon with necessary information to guide the electrode.
The resectoscope electrode tip is an "active" electrode. In a typical system, a complete circuit is formed with a plate-like "dispersive" or grounding electrode often placed in contact with a relatively wide area of the patient's back. The grounding electrode is coupled to the active electrode via a voltage generator for creating a potential between these two electrodes. A wide variety of voltages, frequencies, patterns, etc. may be involved depending upon the application and the choices of the equipment designer and surgeon. Tissue cutting or removal may then be accomplished by arcing between the active electrode and the patient's tissue or by resistive heating of the patient's tissue in contact with the active electrode.
Broadly defined, two major classes of electrodes are cutting electrodes and desiccation electrodes. In the latter, the electrode tip interacts with a tissue surface within the patient. In the former, the electrode is typically formed as a wire loop which is typically used to make a penetrating cut. The loop may be plunged beneath the tissue surface and then moved parallel to the surface to remove a layer of tissue.
Desiccation electrodes (typically including electrodes designated as "coagulation" electrodes) are drawn over the surface of the tissue in order to desiccate the tissue by resistive heating of the tissue in contact with the electrode tip. Such electrodes generally involve creating a large contact area with the tissue. Many such electrodes feature a spherical electrode surface in contact with the tissue surface. A common configuration of this type of electrode involves a hemispherical shell with its convex surface facing down (toward and in contact with the tissue surface). Another common type is the "roller" electrode which is frequently formed as a right circular cylinder extending transverse to the resectoscope axis and free to pivot about its own central axis. Such an electrode is rolled over the tissue surface by the reciprocation of the working element. The rolling action of the roller-type electrode helps to maintain consistent temperature. However, rolling electrodes often suffer from inadequate electrical contact between the conductor(s) and the rolling element as the contact areas between the two may become corroded or contaminated. Additionally, cylindrical electrodes often suffer from an "edge effect" wherein the current density between the patient and the electrode is concentrated toward the ends of the roller rather than having a more even distribution.
Use of a resectoscope creates a variety of byproducts, including cut and coagulated tissue which must be removed in order to maintain the ease and effectiveness of the procedure. It is also desired to distend the patient's tissues to facilitate the tissue removal procedure. These goals may be accomplished via the introduction of a fluid into the patient. Early use of the resectoscope involved cystoscopy of the bladder. In such a case, the bladder could be filled with a fluid and the procedure performed. At various intervals, the bladder could be drained and refilled. In other applications such as hysteroscopy, there are not the same fluid retention capabilities as exist with the bladder. Accordingly, the continuous flow resectoscope was introduced. A typical continuous flow resectoscope includes an outer tubular sheath and an inner tube concentric therewith. An annular space between the sheath and tube provides an outflow conduit, and an annular space between the tube and telescope provides an inflow conduit for introducing clean fluid to the patient. Such devices are generally described in U.S. Pat. Nos. 3,835,842 and 4,134,406 of Jose J. Iglesias, the disclosures of which are incorporated herein by reference.